(1) Field of the Invention
The present invention relates to a composition comprising a graft-modified polyolefin type elastomer and a polyamide. More particularly, the present invention relates to a resin composition comprising a blend of (a) a graft-modified polyolefin type elastomer and (b) a polyamide, said graft-modified polyolefin type elastomer being partially crosslinked by dynamically heat-treating a mixture of a peroxide-crosslinkable olefin copolymer rubber and an olefinic plastic with an unsaturated carboxylic acid or derivative thereof, an unsaturated epoxy monomer or an unsaturated hydroxy monomer in the presence of an organic peroxide.
(2) Description of the Prior Art
A thermoplastic elastomer has been known as an energy-saving and resource-saving substitute for a cured rubber, and it has been used as automobile parts (bellows, tubes, interior sheets and mudguards), industrial machine parts (pressure-resistant hoses, gaskets and diaphragms), electronic and electric machine parts and construction materials.
As the thermoplastic elastomer, a composition comprising a crystalline thermoplastic polyolefin resin and a cured ethylene/propylene/polyene copolymer rubber is disclosed in Japanese Patent Publication No. 46138/83 or Japanese Patent Publication No. 18448/80. This composition, however, is defective in that the balance between the rubbery elasticity and the mechanical strength is bad.
Furthermore, a thermoplastic elastomer composition comprising a blend of an ethylene/propylene/polyene copolymer rubber, an acrylonitrile/butadiene copolymer rubber, a polypropylene resin and a nylon resin is known from U.S. Pat. No. 4,338,413. This composition has a high oil resistance and other good properties, but the composition is fatally defective in that the resistance against heat aging and the weatherability are poor.
Furthermore, a composition comprising a modification product of a mixture of a polyolefin resin and an ethylene/.alpha.-olefin copolymer with an .alpha.,.beta.-unsaturated carboxylic acid and a polyamide is known from Japanese Patent Application Laid-Open Specification No. 8246/82. This composition is excellent in the mechanical strength, but is poor in the softness, which is one of important properties required for the thermoplastic elastomer.
Namely, a thermoplastic elastomer composition excellent in the oil resistance, the mechanical strength and the resistance against heat aging has not been developed, so far as we know.
A large demand is expected for a polyamide resin as an engineering plastic because the resin has excellent physical properties. However, the polyamide resin is generally insufficient in such properties as the impact resistance at low temperatures, the water resistance and the salt water resistance, and it is desired that these properties will be improved. As the means for improving impact resistance characteristics, prior art references such as Japanese Patent Publication No. 12546/67, Japanese Patent Publication No. 44108/80, Japanese Patent Application Laid-Open Specification No. 9962/80 propose methods in which a modified .alpha.-olefin elastic copolymer such as an ethylene/.alpha.-olefin copolymer grafted with an .alpha.,.beta.-unsaturated carboxylic acid is incorporated into a polyamide resin. The compositions proposed in these prior art references are defective in that if the impact resistance characteristics such as the Izod impact strength are improved, the rigidity is drastically reduced, the falling weight impact strength at low temperatures is insufficient, and practical molded articles having a high rigidity and a high impact strength can hardly be obtained from these compositions. Furthermore, the melt flowability is often reduced excessively, and the compositions are defective in that the moldability and processability are degraded in some molding methods.
As a composition in which the foregoing defects are eliminated, that is, a polyamide composition in which the impact resistance and the rigidity are well-balanced, there is proposed a resin composition comprising a polyamide resin and a modified polyolefin obtained by grafting an ethylene/.alpha.-olefin copolymer having a crystallinity lower than 35%, which is obtained by using a specific catalyst, with an unsaturated carboxylic acid or a derivative thereof (see Japanese Patent Application Laid-Open Specification No. 147008/84). However, even if this specific modified polyolefin is used, the improvements of the rigidity, the tensile strength and the like are still insufficient.